Decaffeination of Coffee

Abstract

Coffee is the third most popular beverage in the world after tea and water. However, the caffeine within coffee prevents some people from enjoying the strength, taste, and aroma that this beverage has to offer. In the past century, a new market for decaffeinated coffee has arisen, and the technology to develop this product has evolved. Over time, this technology has become more effective in removing a greater percentage of caffeine, while preserving more of the coffee’s flavour. Because of these advances, about 12% of coffee consumed in the world today is decaffeinated (Clydesdale 1999).
This Report focuses on the methods of decaffeinating coffee, first providing a brief history of the processes used, and then transitioning into the current methods of decaffeination. The processes analyzed include solvent-based decaffeination, water decaffeination, and a supercritical carbon dioxide process. A brief description of each process is provided and then the processes are contrasted based on the following criteria: effectiveness of removing the caffeine, preservation of the coffee’s flavour, and relative cost of the process. After reading this report, one should have a basic knowledge of the decaffeination process, as well as be able to make an informed decision about which decaffeination process is best.

Introduction
Coffee is one of the most popular beverages in the world, but to some people, the caffeine within coffee is undesirable. Caffeine can cause insomnia, migraines, increased blood pressure and addiction symptoms along with many other health detriments (Hyman 2012). For this reason, many people have started turning to decaffeinated coffee. Today, decaffeinated coffee accounts for about 12% of the world’s total coffee consumption (Clydesdale 1999). With this growing market, many different industrial decaffeination techniques have developed.
Decaffeination processes must remove the caffeine from coffee while preserving the coffee’s unique flavour. Also, all decaffeination is done before roasting the beans, while keeping the whole bean intact. Under these constraints the processes have slowly developed and have been optimized over time
Decaffeination Processes
Origins of Decaffeination
The first decaffeination process was invented by Ludwig Roselius in 1905 (Clydesdale). He found that soaking coffee beans in benzene removed the caffeine from coffee while leaving the flavour relatively untouched. With this discovery, he created an industrial decaffeination process similar to the solvent-based process used today. Unfortunately, benzene is slightly toxic in humans, and so the process was eventually discontinued. Even though the process Roselius used was flawed, his work led to the development of modern decaffeination techniques.

Solvent-Based Decaffeination
Solvent-based decaffeination evolved naturally from the original decaffeination process. It involves using a methylene chloride or ethyl acetate solvent to extract the caffeine from the coffee beans. These solvents work well because they are relatively selective for the caffeine and thus leave the flavours of the coffee intact. The actual decaffeination process can occur in either a direct or indirect solvent extraction process.
Extractors
Coffee Beans In
Decaffeinated Beans
Evaporator
Caffeine
Solvent
Solvent with Caffeine
Extractors
Coffee Beans In
Decaffeinated Beans
Evaporator
Caffeine
Solvent
Solvent with Caffeine

Figure 1: Direct Solvent-Based Decaffeination
In the direct decaffeination process (Figure 1), the solvent comes into direct contact with the uncooked coffee beans. The beans are then given time to soak in a series of extraction tanks, thus removing the majority of the caffeine from the beans. This caffeine-rich solvent is then sent to an evaporator where the solvent may be evaporated off and recycled back into the process. The unevaporated caffeine residue can then be removed and either discarded or further purified.

Figure 2: Indirect Solvent-Based Decaffeination (Brennecke 2002)
In the indirect decaffeination process (Figure 2), the solvent never actually comes into contact with the coffee beans. Instead, water is used to extract the caffeine along with all of the aromas and flavours of the coffee bean. This water then passes over the solvent where the caffeine is removed from the water, but the flavour of the coffee remains within the water. This water is then reintroduced to the flavourless beans, which then reabsorb all of their lost flavour. Upon drying the beans, one obtains the decaffeinated coffee product.
The solvent-based decaffeination processes boast a 96-97% removal of the caffeine originally present within the beans (Brennecke 2002). In addition to this, the flavour loss for the process is relatively small due to the selectivity of the solvents. Overall solvent-based decaffeination is an effective and widely used process.

Water Decaffeination
Water decaffeination has many of the same characteristics as its solvent-based counterpart, except that water is used as the solvent. Of course, using pure water alone would absorb the flavours of the coffee along with the caffeine, and so the water used must be properly treated first. The water is first soaked in green coffee beans, where it absorbs all of the flavours and caffeine of the green coffee extract. Next this water passes over a bed of activated charcoal, which absorbs the caffeine but leaves the flavours within the water. This flavour-filled water is then ready to be used in the process.

Figure 3: Water Decaffeination Process
The water decaffeination process (Figure 3) involves soaking uncooked coffee beans in this pre-treated water in a series of extraction units. The water will absorb the caffeine from the beans, but will leave the flavor within the coffee, as the water is already saturated with the flavors from the green coffee extract. The water is then sent to an absorption chamber where it again passes over activated charcoal to remove its caffeine. This water may then be recycled back into the extraction tanks. This process is the least effective at removing caffeine as it removes 94-96% of the original caffeine in place (Clydesdale 1999). Also, some of the flavour of the coffee is lost to the bed of activated charcoal during the process. Despite these drawbacks, this is also the least expensive process as it simply uses water as a solvent. Overall, water decaffeination is the least effective process, and for that reason has seen a diminishing use in industry over time.

Supercritical Carbon Dioxide Process
Using supercritical carbon dioxide to remove caffeine from coffee is the most recent and technology intensive decaffeination process used today. Supercritical carbon dioxide is carbon dioxide pressurized to 250-300 bar, giving it the properties of a supercritical fluid. It exhibits a density similar to that of a liquid, but the viscosity and diffusivity like that of a gas (Perry). These properties, along with the carbon dioxide’s selectivity for caffeine, make supercritical decaffeination possible.
The supercritical carbon dioxide process (Figure 4) involves passing a high pressured carbon dioxide fluid over the coffee beans. Due to its properties, this supercritical fluid can easily penetrate the beans to remove the caffeine, while leaving the flavours of the coffee intact. This supercritical fluid, now rich in caffeine, is fed through water within a column, which then absorbs most of the caffeine from the carbon dioxide. The caffeine lean carbon dioxide is then free to be recycled back into the process.

Figure 4: Supercritical CO2 Decaffeination (Beckman 2004)
One unique aspect about this carbon dioxide process is that high purity caffeine may be recovered as a side product. This is done when the caffeine rich water undergoes reverse osmosis to produce a concentrated caffeine product (Figure 4). This caffeine can then be sold to pharmaceutical companies or soft drink manufacturers who are in need of this high purity caffeine.
The supercritical carbon dioxide process is the most effective at removing caffeine of all current decaffeination processes at an astonishing 97-98% removal of original caffeine (Beckman 2004). Also, the selectivity of the carbon dioxide allows for a nearly negligible loss in the flavour of the coffee. The only major drawback of the process is the steep capital cost of equipment necessary to maintain the high pressures the process operates at. Overall, the supercritical carbon dioxide process is the most effective method of decaffeination, as long as one can afford the massive initial investment required.

Summary
The market for decaffeinated coffee has gradually increased over time, and with it, decaffeination processes have been developed. All modern decaffeination techniques involve using a fluid to extract the caffeine from uncooked coffee beans. The water decaffeination process is the least expensive but also the least effective. Both direct and indirect solvent-based decaffeinations have a moderate effectiveness, as well as a moderate cost associated with the processes. The supercritical carbon dioxide process is far superior to the other processes, but also incurs the highest expenditure.

References
Beckman, Eric J. (2004) “Supercritical and near-critical CO2 in green chemical synthesis and processing” In The Journal of Supercritical Fluid. Volume 28, Issue 2. Pittsburgh, PA: University of Pittsburgh.
Brennecke Joan F. and Stadtherr Mark A. (2002). “A course in environmentally conscious chemical process engineering” in Computers & Chemical Engineering. Volume 26, Issue 2. Notre Dame, IN: University of Notre Dame.
Clydesdale, Fergus. (1999). How is caffeine removed to produce decaffeinated coffee? October 1999. New York: Scientific American. http://www.scientificamerican.com/article.cfm?id=how-is-caffeine-removed-t
Hyman, Mark. (2012). Ten Reasons to Quit Your Coffee. Lenox, MA: Ultrawellness. http://drhyman.com/blog/2012/06/13/ten-reasons-to-quit-your-coffee/
Perry, Robert H. and Green, Don W. (2008). Perry’s Chemical Engineers’ Handbook. 8th ed. Toronto: McGraw-Hill.

References: Beckman, Eric J. (2004) “Supercritical and near-critical CO2 in green chemical synthesis and processing” In The Journal of Supercritical Fluid. Volume 28, Issue 2. Pittsburgh, PA: University of Pittsburgh. Brennecke Joan F. and Stadtherr Mark A. (2002). “A course in environmentally conscious chemical process engineering” in Computers & Chemical Engineering. Volume 26, Issue 2. Notre Dame, IN: University of Notre Dame. Clydesdale, Fergus. (1999). How is caffeine removed to produce decaffeinated coffee? October 1999. New York: Scientific American. http://www.scientificamerican.com/article.cfm?id=how-is-caffeine-removed-t Hyman, Mark. (2012). Ten Reasons to Quit Your Coffee. Lenox, MA: Ultrawellness. http://drhyman.com/blog/2012/06/13/ten-reasons-to-quit-your-coffee/ Perry, Robert H. and Green, Don W. (2008). Perry’s Chemical Engineers’ Handbook. 8th ed. Toronto: McGraw-Hill.